1. Field of the Invention
The present invention relates to a rotary encoder for detecting rotation information such as a rotational speed and a rotational angle of an object to be detected, in particular a rotary encoder suitable for detecting a rotational angle original point of the object to be detected.
2. Description of the Related Art
As a rotary encoder, there is known an optical rotary encoder adapted for detecting absolute position information among rotation information about an object to be detected (Japanese Patent Application Laid-Open No. 2006-214929). For example, in a reflecting type rotary encoder, light emitted from a light emitting element such as an LED provided on a detecting head is reflected by a rotary scale, the returning light is received by a light detecting element such as a phototransistor, and lights and darks of the received light are counted, thereby measuring the rotation information about the rotary scale.
The rotary encoder of a type which detects an absolute position (position of an original point) is, in many cases, fabricated by aligning an original point of a rotational angle of the rotary scale with a predetermined position on a rotating body, for example a hub, and performing adjustment by visual inspection or the like. Similarly, a pattern center of the rotary scale and a rotation center of the hub also require a similar adjustment. In this case, centering is achieved by processing a hole and the pattern center of the scale with high accuracy so as to make a clearance relative to a fitting portion of the hub smaller and thus suppressing eccentricity.
As regards the reflecting type rotary encoder, in the rotary scale involving a function of detecting the position of the original point, reflecting portion patterns are radially arranged at regular intervals with respect to the pattern center. A part of those patterns is eliminated to provide a missing portion for detecting the position of the original point, which has no reflecting portion pattern. This missing portion is detected by a detecting head, thereby defining a rotational angle original point. However, because the rotary scale is disc-shaped and difficult to determine its mounting phase, there is a problem in that, in order to align the original point of the rotary scale with the hub with regard to the original point of the angular direction and to assemble the rotary scale and the hub, many hours for these processes are required. Further, there is a problem in that centering between the rotary scale and the hub also requires many hours or needs improvement for accuracy of an inner diameter of the rotary scale, which leads to prolonged production time.